Chronic human inflammatory bowel diseases (IBD), such as Crohn?s Disease and Ulcerative Colitis, afflicts approximately two million individuals in this country alone. These disorders are primarily characterized by the presence of activated forms of T lymphocytes in the intestinal mucosal compartment. Through a number of investigations in murine models of IBD, as well as human studies, it is becoming increasingly recognized that IBD is associated with luminal or environmental stimuli in a genetically susceptible host. One of the best-characterized murine models of IBD is the CD45RBhigh CD4+ T cell transfer model. Adoptive transfer of this particular subset of T cells into a severe combined immunodeficient (SCID) congeneic recipient, who lacks functional B or T cells, results in colitis. However, adoptive transfer of the CD45RBlow CD25+ CD4+ T cells inhibits colitis. Recent evidence indicates that both T cell subsets are dependent on MHC class II and are activated through a restricted set of T cell receptors, which indicates expansion to a limited set of antigens. The model is also dependent on environmental antigen exposure, as SCID mice raised under germ-free conditions, do not develop colitis following cell transfer. Taken together, this implies that the effector and regulatory CD4plus T cells in this transfer model of colitis are most likely activated by a limited number of peptide antigens presented in a MHC class II dependent fashion, and possibly derived from the luminal environment. Therefore, the primary goal of this project is to elucidate the peptide antigen(s) involved in the CD45RBhigh CD4+ T cell population effector response or the CD45RBlow CD25+ CD4+ inhibitory response. Specifically, we plan to use a methodological approach involving cDNA expression libraries to identify unknown peptide antigens for these subsets of T cells. Preliminary experiments with murine DO11.10 CD4+ T cell hybridoma cells, which recognize a 17 amino-acid peptide epitope of chicken ovalbumin in the context of MHC class II, has indicated the initial parameters of this methodology. The primary goal is to identify expressed peptide(s) from recombinant fusion proteins created from cDNA libraries made from tissue and cecal bacteria extracts. The libraries will be screened for reactive epitopes by proliferation and cytokine production. Next, these important T cells will undergo T cell receptor evaluation. Potentially, by this approach, antigens responsible for CD45RBhigh CD4plus T cell adoptive transfer model of colitis can be elucidated, this may lead to a better understanding of human inflammatory bowel disease.